Zinc Oxide nanowires flower for Magnolia Optical Technologies

Iraqi snipers have improved  since the US invasion, but so has countersniper technology. Acoustic detectors, laser spotters and infrared sensors have improved US troops' ability to zero in on enemy sharpshooters. Now nanotechnology promises to produce a generation of much more sensitive sniper-spotters.

"It's very exciting material," says Ashok Sood, president of Magnolia Optical Technologies,  who plans to use them to build sensors for detecting the ultraviolet light generated by gunshots in battle to pinpoint sniper locations.

In April, Magnolia was awarded a $500,000 contract by the US Army and the Defense Advanced Research Projects Agency (DARPA) to continue work on the sniper sensors. So far, the small, high-tech firm in Woburn, Massachusettes., has received $1.25m in DARPA research contracts for the effort.

Gunfire emits a flash of ultraviolet light that cannot be seen by the human eye, but can be detected by ZnO nanowires. When struck by ultraviolet photons, the nanowires convert energy from the photons into tiny electrical signals.  A computer processes the signals inform soldiers where the sniper is located

Sensors that use ZnO nano-wires may be thousands of times more sensitive than infrared sensors, said Zhong Wang, a leading nanotechnology researcher and professor at Georgia Tech's Center for Nanostructure Characterization.

Wang is working with Magnolia Optical on the sensors. Sood said he hopes to have a prototype ready for the Army as early in a year from now. Besides spotting snipers, such sensors are expected to prove valuable for detecting other battlefield sources of ultraviolet light such as missiles and jet aircraft.

As they burn fuel, rocket and jet engines emit invisible but detectable plumes of ultraviolet light. Sensors built on ZnO nano-wire technology are expected to be more sensitive than current UV sensors.

The ability to convert light into electricity also makes ZnO nanowires an attractive material for use in solar cells, Sood said. Magnolia is working with Kopin Corporation on a second phase space solar cells where the company's novel coating technologies will be used to prevent sunlight reflecting off the cells diminishing performance and also to lengthen the life of the solar cells in space radiation conditions.

The tubular shape of the ZnO wires gives them much greater surface area for absorbing sunlight, and the nanowires provide a more efficient means to shuttle electrons to the solar cell's electrodes as light is converted into electricity. ZnO nanowires can also convert electricity into light.

Sood says that when electricity is applied to them, the nanowires can be turned into light-emitting diodes - LEDs emitting "very bright ultraviolet light." One use might be for battlefield water purification, he said. Exposing water to the ultraviolet light for about five minutes kills the bacteria in it. Siimilarily, ZnO nano-wires may be used to produce lasers.

Jia Grace Lu, a researcher at the University of Southern California, says the nanowires could  be used to make sensors for detecting dangerous chemicals. ZnO nanowires are basically semiconductors; that is, their ability to conduct changes under certain conditions. When exposed to different chemicals, conductivity increases or decreases depending on the substance.

In the presence of carbon mon-oxide, for example, ZnO nano-wires become more conductive. In the presence of nitrogen dioxide, however, their ability to conduct electricity decreases. According to Lu, ZnO nano-wires respond to the presence of different chemicals "with exquisite precision" So by measuring the changes in conductivity, it should be possible to determine what chemicals are present.
Piezoelectronic Zno nanowires.

In the most eye-catching recent development,
Georgia Tech announced in February that Wang's research group had developed textile fibers that contain ZnO nanowires, and that clothing made from the fibers would turn motion from the wearer into electricity.

"If we can combine many of these fibers in double or triple layers in clothing, we could provide a flexible, foldable and wearable power source that, for example, would allow people to generate their own electrical current while walking," Wang said at the time.

With uniforms that incorporate ZnO nanowires, soldiers might recharge batteries or power small electronic devices. The nanowires possess "piezoelectric" properties. That is, bending them creates electricity. As each wire is bent, there is a positive charge on one side and a negative charge on the other. When straightened, a tiny electrical current is produced.

Wang dubbed the current-producing nanowires as "nanogenerators." But power-producing clothing is not in the stores or on the battlefield yet. They're "very new. We still have a lot of work to do" to prepare them for real-world applications," Wang said.

Source: http://www.magnoliaoptical.com/

Above Piezoelectric nanowires: Courtesy: http://twenty1f.com/ The researchers, led by materials-science professor Zhong Lin Wang, have made a flexible fiber coated with ZnO nanowires that can convert mechanical energy into electricity. The fibers, the researchers say, should be able to harvest any kind of vibration or motion for electric current. The zinc oxide nanowires grow vertically from the surface of the polymer fiber. When one fiber brushes against another, the nanowires flex and generate electric current. The researchers described a proof-of-concept yarn in a paper published in the journal Nature. They show that the output current increases by entwining multiple fibers to make the yarn. By the researchers’ calculations, a square meter of fabric made from the fibers could put out as much as 80 milliwatts–enough to power portable electronics. The development could make shirts and shoes that power iPods and medical implants, curtains that generate power when they flap in the wind, and tents that power portable electronics devices.

'Flaming' Nanowires
The unique branched growth of these zinc oxide (ZnO) nanowires was produced using vapour transportation methods. ZnO, which exhibits a direct bandgap of 3.37 eV at room temperature with a large exciton binding energy of 60 meV, is of considerable technological importance because of its potential use in short-wave devices, such as ultraviolet (UV) light-emitting diodes and laser diodes. In particular ZnO nanowires have been demonstrated in room-temperature UV lasing, and individual ZnO nanobelts have been demonstrated as field-effect transistors (FETs) and nanosensors.
Courtesy: http://www.msm.cam.ac.uk